Population growth and development of the psocid Liposcelis rufa (Psocoptera: Liposcelididae) at constant temperatures and relative humidities

We investigated the effects of eight temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, and 40.0 degrees C) and four relative humidities (43, 55, 63, and 75%) on population growth and development of the psocid Liposcelis rufa Broadhead (Psocoptera: Liposcelididae). L. rufa did not survive at 43% RH, at all temperatures tested; at 55% RH, at the highest four temperatures; and at 63% RH and 40.0 degrees C. The greatest population growth was recorded at 35.0 degrees C and 75% RH (73-fold growth). At 40.0 degrees C, L. rufa populations declined or barely grew. L. rufa males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 31, 54, and 15%, respectively. Female L. rufa have two to five instars, and the percentages of females with two, three, four, and five instars were 2, 44, 42, and 12%, respectively. The life cycle was shorter for males than females. We developed temperature-dependent developmental equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages. The ability of L. rufa to reproduce at a relative humidity of 55% and temperatures of 22.5-30.0 degrees C and at relative humidities of 63-75% and temperatures of 22.5-37.5 degrees C, in addition to being able to survive at 40.0 degrees C, suggests that this species would be expected to have a broader distribution than other Liposcelis species. These data provide a better understanding of L. rufa population dynamics and can be used to help develop effective management strategies for this psocid.     

Population growth and development of psocid Lepinotus reticulatus at constant temperatures and relative humidities

We investigated the effects of temperature and relative humidity on population growth and development of the psocid Lepinotus reticulatus Enderlein. Part of this study assessed the effects of marking psocids by using methylene blue, chalk powder, and fluorescent powder to differentiate nymphal stages during development. We found that marking psocids by using methylene blue increased mortality and took twice as long to accomplish compared with marking by using fluorescent powder. Using chalk powder shortened the duration of third and fourth nymphal instars. Marking psocids by using fluorescent powder had no effect on mortality or duration of nymphal instars. Therefore, we recommend using fluorescent powder for marking psocids. L. reticulatus did not survive at 32, 43, and 55% RH, whereas populations increased from 22.5 to 32.5 degrees C at 75% RH. The largest population growth was recorded at 30 and 32.5 degrees C, whereas only 9% of nymphs developed to adults and populations declined at 35 degrees C. We developed temperature-dependent developmental equations for eggs, individual nymphal, combined nymphal, and combined immature stages. These equations showed predicted optimal temperatures for the development of eggs, combined nymphal, and combined immature stages to be 32.3, 34.5, and 34.4 degrees C, respectively; development at these temperatures was completed in 6.3, 16.7, and 23.3 d, respectively. Our study shows that psocids that consume their exuviae develop faster than those that do not, and this effect is more pronounced at lower temperatures. These data give us better understanding of L. reticulatus population dynamics, and they can be used to develop effective management strategies for this psocid.     

Development, survival, and reproduction of the psocid Liposcelis yunnaniensis (Psocoptera: Liposcelididae) at constant temperatures

We investigated the effects often constant temperatures (20.0, 22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, 39.0, and 41.0 degrees C) on the development, survival, and reproduction of the psocid Liposcelis yunnaniensis Li & Li (Psocoptera: Liposcelididae). At 39.0 and 41.0 degrees C, none of individuals could develop successfully or reproduce. From 20 to 37.5 degrees C, the development period from egg to adult ranged from 64.3 d at 20 degrees C to 16.1 d at 35 degrees C. The lower developmental threshold for egg, nymph, and combined immature stages were estimated at 15.08, 15.13, and 14.77 degrees C, respectively. After emergence the females went through a preoviposition period that ranged from 18.5 d at 22.5 degrees C to 3.11 d at 35 degrees C, whereas it was 16.3 d at 20 degrees C. Liposcelis yunnaniensis produced most eggs at 35 degrees C and the fewest at 22.5 degrees C. The population reared at 35 degrees C had the highest intrinsic rate of increase, shorter mean generation time, and shortest population doubling time compared with other temperatures. According to Weibull frequency distribution, L. yunnaniensis reared at all the temperatures had type III survivorship curves (c < 1.0). Based on life-table parameter estimations, we suggest that optimum range of temperatures for this species is from 25 to 37.5 degrees C. These data give us useful information on population biology of L. yunnaniensis and can be used to better manage this species.     

嗜虫书虱种群增长模型的研究

【目的】构建嗜虫书虱Liposcelis entomophila (Enderlein)在不同环境条件下的种群增长模型,为粮库书虱种群预测预报提供基础数据和理论模型。【方法】通过构建嗜虫书虱实验种群生命表,分析温度、湿度、食物破碎率和种群初始密度对嗜虫书虱种群数量动态的影响,验证种群的指数增长模型,并拟合温湿度与内禀增长率的函数关系。【结果】在温度26-34℃,湿度65%-85%,食物破碎率4%-12%的条件下,温度和湿度对发育历期有显著影响,三者对种群数量趋势指数、净增殖率、内禀增长率的影响均不显著。三者对种群增长影响的主次顺序为:温度>湿度和食物破碎率。嗜虫书虱种群增长的最适条件为温度34℃、相对湿度85%、食物破碎率12%。当种群初始密度为0.26-1.04头/cm2时,嗜虫书虱种群数量呈指数增长。【结论】在22-34℃,相对湿度65%-85%的环境中,嗜虫书虱种群数量动态与温度和湿度的关系可以拟合为Nt=N0EXP[(0.002 96T+0.021 67RH-0.037 2)t]。     

三色书虱体内共生微生物Wolbachia的wsp基因的分子检测

采用常规PCR和巢式PCR方法对三色书虱Liposcelis tricolor体内的共生微生物Wolbachia的wsp基因进行分子检测;通过Wolbachia的通用引物以及A、B亚群引物分别比较了常规PCR和巢式PCR对wsp基因扩增的灵敏性。从三色书虱体内扩增出了610bp的Wolbachia的wsp基因片段,500bp的WolbachiaA亚群的wsp基因片段和450bp的Wolbachia B亚群的wsp基因片段。扩增结果说明三色书虱被A和B两个亚群的Wolbachia混合感染;巢式PCR比常规PCR更为灵敏。     

储藏物害虫嗜卷书虱对DDVP熏蒸的行为反应与致死剂量

1 引言 嗜卷书虱(Liposcelis bostrychophila)属啮虫目虱啮科。其体形微小,食性复杂,栖息场地多在粮食仓库及食品加工厂、图书馆、标本馆等地。大量发生时可造成严重损失,传播微生物,并以其尸体、排泄物等污染储藏的粮食和其它储藏物品。王进军等调查发现,在我国“双低”和“三低”贮粮的粮仓中,书虱已成为优势种群,对贮粮安全构成了威胁。使用病原真菌和细菌来防治嗜卷书虱,很难达到理想效果,即使采用菊酯类杀虫剂也难以奏效,贮粮熏蒸中普遍使用的溴甲烷(CH_3Br)和磷化氢(PH_3)对嗜卷书虱的防治效果也不很理想。利用昆虫生长调节剂防治嗜卷书虱的研究已有一些报道,但在具体应用上还存在着一些问题。气调措施可应用于控制书虱种群的增长,但书虱的抗气性发展很快,     

两种昆虫生长调节剂对嗜虫书虱的致死作用

系统测定了灭幼宝（Pyriproxyfen)和烯虫酯（Methoprene) 2种昆虫生长调节剂对储藏物主要害虫嗜虫书虱（Liposcelis entomophila)的生物活性。采用饲料混药法,针对不同浓度的灭幼宝和烯虫酯分别对嗜虫书虱若虫的致死作用,对若虫发育历期,成虫繁殖力和卵孵化率的影响设置不同处理和重复。结果表明,灭幼宝对嗜虫书虱若虫的致死作用非常明显,其效果比烯虫酯好;不同浓度的灭幼宝使若虫的发育历期明显延长; 灭幼宝和烯虫酯对嗜虫书虱的成虫无杀伤作用,但对成虫的产卵量有明显的抑制作用,两者的作用浓度却相差5倍。灭幼宝对卵的孵化率影响更大,因而具有更显著的杀卵效果。     

Survival and reproduction of Liposcelis paeta (Pearman) (Psocoptera: Liposcelididae) when irradiated by electron beams

Electron beam irradiation has been evaluated for the survival and reproduction of Liposcelis paeta Pearman (Psocoptera: Liposcelididae). All effects increased with increasing doses from 50 to 1000 Gy when the electron energy was 2 MeV. Eggs were unable to develop into adults following a dose of 100 Gy. Complete (100%) mortality was achieved about 5 weeks after adult emergence from nymphs irradiated at 300 Gy, whereas 100% mortality of adults was achieved 9 weeks after irradiation at 300 Gy. The fecundity was greatly reduced to 1.82% of that of control when L. paeta adults were irradiated at 250 Gy. A dose of 300 Gy caused complete reproductive sterility in adults. These results suggest that the most susceptible stage was the egg stage, then nymph and adult stages. A dose of 300 Gy is suggested for quarantine treatment of commodities infested by L. paeta.     

Molecular characterization of two nicotinic acetylcholine receptor subunits from Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae)

Two nicotinic acetylcholine receptor (nAChR) subunit genes, Lbα1 and Lbα8, were isolated and characterized from psocid, Liposcelis bostrychophila Badonnel, using the rapid amplification of cDNA ends (RACE) technique. They are the first two nAChR family members isolated from the insect order of Psocoptera. The full‐length cDNAs of Lbα1 (GenBank accession number: EU871527) and Lbα8 (EU871526) consist of 2,025 and 1,763 nucleotides, respectively, and an open reading frame of 1,644 and 1,608 bp encoding 547 and 535 amino acid proteins, respectively. Both genes have typical features of nAChR family members, though they share only 56% identity in amino acid sequence. The dendrogram generated by the MEGA 3.1 program shows that the protein deduced by Lbα1 had the closest phylogenetic relationship to Agamα1 from Anopheles gambiae and Amelα1 from Apis mellifera, and Lbα8 shares the highest identity with Agamα8 from An. gambiae and Amelα8 from A. mellifera. Quantitative real‐time PCR analysis showed that Lbα1 was expressed 2.03–6.54‐fold higher than Lbα8 at the different developmental stages of L. bostrychophila. The highest expression levels of Lbα1 and Lbα8 were both detected at adult stage and the lowest were at the third and fourth nymphal stages, respectively. There was a stable and relatively low expression level for Lbα1, whereas there was a descending expression pattern for Lbα8 in the 1st through the 4th nymphal stadia. © 2009 Wiley Periodicals Inc.     

Tracing the geographic origin of the cosmopolitan parthenogenetic insect pest Liposcelis bostrychophila (Psocoptera: Liposcelididae)

The randomly amplified polymorphic DNA technique was used to trace the geographic origin of Liposcelis bostrychophila Badonnel populations in Australia from unknown geographic sources internationally. Haplotype (or clonal) diversity was high, with 474 unique haplotypes found from 616 individuals genotyped. Gene diversity estimates (0.10-0.28) and percent polymorphic loci (38.1-88.1%) were moderate to high for most populations. This resulted in genetic distance estimates that ranged from 0.04 to 0.26 and were significantly different for most pairwise population combinations. G ST values for all populations were also moderate (0.04-0.54) and again were significantly different for most pairwise population comparisons. Analysis of molecular variance revealed that the majority of variation was apportioned among individuals within populations regardless of the level at which they were grouped. Gene flow (Nm) was mostly low for all pairwise populations comparisons with an average Nm=1.8. A non-significant negative correlation between genetic distance and geographic distance was found for worldwide populations. In contrast, within Australian populations a significant positive correlation between genetic distance and geographic distance was detected. Genetic relationships explored using unweighted pair group method analysis and non-metric multidimensional scaling indicated a mixed pattern of genetic similarities among all populations. Multiple introductions, from a wide range of international source populations, have obscured the ability to accurately determine the geographic origin of L. bostrychophila in Australia.     

Influence of wolbachia infection on the fitness of the stored-product pest Liposcelis tricolor (Psocoptera: Liposcelididae)

Wolbachia are maternally inherited intracellular bacteria (Rickettsiaceae) that infect a wide range of arthropods and nematodes and that are associated with various reproductive abnormalities in their hosts. In this study, the effects of removal of Wolbachia infection on development, survival, and reproduction of Liposcelis tricolor Badonnel (Psocoptera: Liposcelididae) were investigated in laboratory. The Wolbachia-free strain was obtained by the removal of Wolbachia infection by using 1% rifampicin treatment on the Wolbachia-infected strain (control) for 4 wk, and no Wolbachia gene product was detected in this strain throughout the experiment. The results showed that the removal of Wolbachia infection had negative effects on the fitness of L. tricolor. Compared with the control strain, the Wolbachia-free strain (both in the first [F1] and second [F2] generation) had prolonged developmental times, reduced survivorship of immature stages, and reduced fecundity and longevity, resulting in much smaller rm values. Using rm values, the fitness for Wolbachia-free F1 and F2 relative to the control were calculated as 0.45 and 0.27, respectively. The results of this study further confirmed our previous conclusion that Wolbachia infection have positive effects on fecundity and fertility of L. tricolor, and for optimal reproduction of L. tricolor, Wolbachia must be present in psocids.     

Volatile compounds from Liposcelis bostrychophila (Psocoptera: Liposcelididae) and their environment and their effects on settling behaviour

Headspace from above either Liposcelis bostrychophila Badonnel reared on powdered food; insects without food or from powdered food only were collected on five occasions over a period of four weeks. Volatiles were analysed by thermal desorption gas chromatography-mass spectrometry (TD-GCMS) to look for ecologically significant volatile compounds. Hexanoic acid (HA) was the major compound in the insect only and diet only volatiles (insect 25.6 ± 1.6%, diet 32.9 ± 1.13%). Isobutyric acid was the main compound detected in the volatiles from both insects and diet (35.3 ± 6%). Butyric acid (BA) and acetoin (HB) were also present at >2% of the total peak areas. HB was not detected in the insect only volatiles. Bioassays showed that hexanoic acid was the most repellent chemical. Mixtures of compounds representing the proportions of HA, BA, IBA, and HB in the volatiles did not have any prolonged effect on settling or selection by booklice in a two choice bioassay. L. bostrychophila can avoid individual volatile chemicals but the effects can be masked when they are incorporated into mixtures. As some volatile compounds can be detected by booklice they may govern dispersal, but further work is required to clarify their significance.     

Purification and partial characterization of glutathione S-transferase from insecticide-resistant field populations of Liposcelis paeta Pearman (Psocoptera: Liposcelididae)

Enzymes that possess glutathione S-transferase (GST) activity were purified to homogeneity by glutathione-agarose affinity chromatography from three field populations of Liposcelis paeta (Pearman). These populations were collected from Nanyang city of Henan Province (NY), Wuzhou (WZ) and Hezhou (HZ) cities of Guangxi Province, China, and had different susceptibilities to dichlorvos [LC₅₀s of the NY (281.48 mg/m²), the WZ (285.07 mg/m²), and the HZ (243.52 mg/m²), respectively]. The specific activities of purified enzymes from these three populations increased 32.24-, 99.81-, and 42.52-fold, respectively. Kinetic analyses showed that the catalytic activity of purified GST from NY population towards GSH was much higher than the others, while WZ population reached the highest in V. SDS–polyacrylamide electrophoresis revealed that the purified GST had two subunits with a molecular mass of 23.31 and 20.43 kDa for NY, 53.14 and 20.13 kDa for WZ, and 50.79 and 19.42 kDa for HZ, respectively. The in vitro inhibition studies of GSTs indicated that three kinds of insecticides (chlorpyrifos, carbosulfan, and cypermethrin) and five metallic ions (Zn²⁺, Ba²⁺, Ca²⁺, Hg²⁺, Mn²⁺, and Mg²⁺) all possessed inhibitory effects on purified GST, and ethacrynic acid (EA, a specific inhibitor of GST) expressed inhibitory effects. In the bioassay, three populations of L. paeta had different susceptibilities to different insecticides, even after they were reared on diets consisting of 25% EA. The GST activities of L. paeta from different areas also showed different temperature and pH stabilities. The differences in GST among the three populations may be attributed partially to the differences in control practices for psocids between Henan and Guangxi Provinces. © 2009 Wiley Periodicals, Inc.     

Cloning and characterization of acetylcholinesterase 1 genes from insecticide-resistant field populations of Liposcelis paeta Pearman (Psocoptera: Liposcelididae)

The psocid, Liposcelis paeta Pearman, is an increasingly important polyphagous pest of stored products worldwide. Intensive use of organophosphorous insecticides for pest control has facilitated resistance development in psocids in China. Three insecticide-resistant field populations of L. paeta were collected from Nanyang city of Henan Province (NY), and Wuzhou (WZ) and Hezhou (HZ) cities of Guangxi Province, China. Previous studies have shown that psocids have different susceptibilities to insecticides. In addition, their AChE susceptibilities to paraoxon-ethyl and demeton-S-methyl also differed from each other. Acetylcholinesterase 1, which is one of the major targets for organophosphate insecticides, has been fully cloned and sequenced from these populations of L. paeta. Comparison of both nucleotide and deduced amino acid sequences revealed nucleotide polymorphisms among L. paeta ace 1 genes from different populations, but none of these polymorphisms correspond to the active sites in AChE 1 from other insects. The results of comparative quantitative real-time PCR indicated that the relative expression level of HZ ace 1 gene was the highest among three populations, which was 1.20 and 1.02-fold higher than those of NY and WZ populations, respectively. This may due to an epigenetic inheritance phenomenon, which allows organisms to respond to a particular environment through changes in gene expression.     

Effects of removal of Cardinium infection on fitness of the stored-product pest Liposcelis bostrychophila (Psocoptera: Liposcelididae)

Endosymbiotic bacteria that potentially influence reproduction and other fitness-related traits of their hosts are widespread in arthropods, and their appeal to researchers' interest is still increasing. In this study, the effects of removal of Cardinium infection on development, survival, and reproduction of Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae) were investigated in the laboratory. The Cardinium-free strain was obtained by the removal of Cardinium infection by using 1% rifampicin treatment on the Cardinium-infected strain (control) for 4 wk, and no Cardinium gene product was detected in this strain throughout the experiment. The results showed that the removal of Cardinium infection had negative effects on fitness of L. bostrychophila. Compared with the control strain, the Cardinium-free strain (both in first [F1] and second [F2] generation) had a similar developmental time, reduced survivorship of immature stages, as well as reduced fecundity, which resulted in much smaller r(m) values. Using r(m) values, the fitness for Cardinium-free F1 and F2 relative to the control was calculated as 0.81 and 0.74, respectively. We concluded that the use of antibiotics combined with heat treatment might be a good control measure for L. bostrychophila.     

Molecular Characterization and Alternative Splicing of a Sodium Channel and DSC1 Ortholog Genes in Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae)

Alternative splicing greatly contributes to the structural and functional diversity of voltage-gated sodium channels (VGSCs) by generating various isoforms with unique functional and pharmacological properties. Here, we identified a new optional exon 23 located in the linker between domains II and III, and four mutually exclusive exons (exons 27A, 27B, 27C, and 27D) in domains IIIS3 and IIIS4 of the sodium channel of Liposcelis bostrychophila (termed as LbVGSC). This suggested that more alternative splicing phenomena remained to be discovered in VGSCs. Inclusion of exon 27C might lead to generation of non-functional isoforms. Meanwhile, identification of three alternative exons (exons 11, 13A, and 13B), which were located in the linker between domains II and III, indicated that abundant splicing events occurred in the DSC1 ortholog channel of L. bostrychophila (termed as LbSC1). Exons 13A and 13B were generated by intron retention, and the presence of exon 13B relied on the inclusion of exon 13A. Exon 13B was specifically expressed in the embryonic stage and contained an in-frame stop codon, inclusion of which led to generation of truncated proteins with only the first two domains. Additionally, several co-occurring RNA editing events were identified in LbSC1. Furthermore, remarkable similarity between the structure and expression patterns of LbVGSC and LbSC1 were discovered, and a closer evolutionary relationship between VGSCs and DSC1 orthologs was verified. Taken together, the data provided abundant molecular information on VGSC and DSC1 orthologs in L. bostrychophila, a representative Psocoptera storage pest, and insights into the alternative splicing of these two channels.     

Sporulation by Entomophthora schizophorae (Zygomycetes: Entomophthorales) from housefly cadavers and the persistence of primary conidia at constant temperatures and relative humidities

The duration of discharge of Entomophthora schizophorae (Zygomycetes: Entomophthorales) conidia from house fly (Musca domestica, Diptera) cadavers was measured at 7, 18, and 25 degrees C. The higher the temperature, the shorter the duration of conidia discharge. Significantly more conidia were produced per cadaver at 7 degrees C over a period of 120 h than at 18 and 25 degrees C. At 25 degrees C, the initial discharge over the first 10 h was much larger than at the other temperatures, and at 7 degrees C, no peak in discharge was observed. The persistence of E. schizophorae primary conidia was measured on fabricated non-host surfaces typically found in stables (straw, wood, plaster, and glass) at 7, 18, and 25 degrees C or constant relative humidities of 45, 65, and 85%. Persistence, as measured by the subsequent ability to infect flies, was usually only a few days and depended on the temperature and type of surface. It was greatest on straw, followed by wood, glass, and plaster, and at 7 degrees C, followed by 18 and 25 degrees C. Limited transmission took place between flies exposed to conidia and previously unexposed mates.